Rotor winding for asynchronous motors without starters



- 1,682,430 c. SHENFER ROTOR WINDING FOR ASYNCHRONOUS MOTORS WITHOUTSTARTERS Filed Jan. 2, 1925 2 Sheets-Sheet 1 4 fi Q8, C fifft Aug. 28,1928. 2 1,682,430

' C. SHENFER ROTOR WINDING FOR ASYNGHR ONOUS MOTORS WITHOUT STARTERSFiled Jan. 2, 1925 2 sheets-sheet 2 In venfor Patented Aug. 28, 1928.

UNITED STATES PATENT OFFICE. l

ICLAUIDIUS sHEnFER, on Moscow, RUSSIA.

ROTOR WINDING -FOR- ASYNCHRONOUS MOTORS WITHOUT STARTERS.

Application filed January 2, 1923, Serial No. 610,122, and in GermanyMarch 20, 1922. 4

The Gorges system, a method by which asynchronous motors are started upwithout the use of motor starters, and by which the rotor windings areconnected in opposition for the purpose of starting, suffers from thedefect that the 'starting torque of a motor operated under this systemis small. This defect is caused by the low power factor of the rotorcurrents.

The object ofthe present invention is to dispense with startingresistance or other auxiliary apparatus 'as in the Gorges system, and toobtain at the same'time a large starting torque. This is accomplished byimproving the rotor power factor whilst starting, which is brought aboutby-arranging each phase of the 'polyphase rotor winding intwo halveswhich during starting are arranged and connected'in such a manner thatthesetwo halve'sof each phaseoppose and approximately magneticallybalance each other so as to form mainly an ohmic resistance. *Theconnections between the halves 1 of the winding are such that each ofthe two halves thus balanced form part of a circuit through whicheurrent'is caused to flow by an electro-motive force generated in a partless than the half of another phase. This electro-motivc force may bethe whole 'electro-motive force-produced by the part of the half of thephase connected in the said circuit or may be the resultantelectromotive force produced by the action of one half and a part of theother half of thephase mutually opposing and partially balancing. Thetwo mutually opposing halves of each phase preferably have correspondingconductors located in the same slots.

The conversion from the starting to the running condition is effectedwithout opening the rotor circuits, being brought about i simply byapplying short-circuiting -connections to appropriate points so as toproduce the equivalent of a polyphase winding having two or moreshort-circuiting connections between corresponding points of the phases.

. This application of short-circuiting con- V nections can be broughtabout by mechanical devices of well known types such as are employed forobtaining the final short circuit after starting up an asynchronousmotor by the resistance method or'by known devices ment of the rotorwindings for the first method, whilst Figure 3 illustrates'thearrangement of the rotor windings for the second method. 1.

Figure 1' shows the general arrangement of a rotor winding; Figure-2 thearranges mentof a rotor windingfor the gradual speeding up of the motor;Figure 3 the general arrangement of a 'rotor winding;-

' Each rotor phase ishalved and connected as shown in Figure 1. Thefirst phase is formed by half-phases 1 and 1 the second phaseyis formedby half-phases'2 and'2 the third phaseis formed by half-phases 3 and3 Inorder to obtain a high starting torque it is desirable that thecorresponding conductors of the two halves of each phase should bearranged in'the same slots. i In Figure 1 thehalf-phases 1, 2,3 arestar-connected, and the ends of phases 1, 2, 3 remote from thestar-point are connected respectively to the ends of' half phases 1 2 ,3-it'i'1rther fromstar-point 0. -'-The other ends of half-phases 1 2 3?are connected respectively to the mid-points of half-phases 1, 2, 3 sothat there are formed three over lapping closed circuits in whichcurrent is caused to flow by an-electro-inotive force generated only'inapart (0a,'0b 0c) of the half '(1, 2,3) of the phase." These circuitsareas follows duced in the part 0a of the winding is e'f-z fective asthe electro-motive forces induced in halt-phases 3 and 3 neutralize oneanother.

The current i due to the electro-motive tors are arranged'as alreadyindicated. Hence half-phases-ifi, 3 constitute in this case an almostpure ohmic resistance for the current i,--and serve asa startingrheo'stat for part oa of the winding, so 'tliat'the phase displacementbetween the current "iand'the electro-motive force induced in part 0*aot'the winding is'reduced, and the starting'torque of the-motor isincreased. I p

All said wit'hres ect to the circuit o-a 3 3 applies equal y'well tocircuits 0'b-' 1 1-.-and-00 2 2-. H H

With1the-rotor windings connected as in Figure 1 the'stator current atstarting will approximately be equal to one quarter of the short-circuitstator current with the rotor windings connected asfor running while thecurrent Wouldbe onehalf, the electromotive force-generated in the wholehalf winding hfl, 3'wereactive. f-a yet smaller startin current isrequired'thepoints a, b, a, of igure 1 may be moved nearer star-point10. On the other hand a. larger starting current may be obtained bymovingthe points (1,6, 0, further fromstar vpeint n 'T 1 be alteredgradually'by moving the points ll? p y S p- H When arran ed asi Figure 1for start; ,ing purposes fiie connections of the windings may readily bechanged from the starting arrangement to. that of running, afterthemachine has gained speed, simply short-circuiting, step bystepappropriate portions ofthe rotor winding.

Thus, referring to Figure 2, the separate parts ofhalf-phases :1, 2,3,,may be shortcircuited step by step by closing in sequence, as-therotor speeds up, the connections shown ateb 0 those shown at a, b, 0,those shown at aflibfl c ythose shown at a I); c. The result is thathalf phases' 1-1' 22 3'3 respectively no longer compensate one anothermagnetically, and so the ohmic resistance (ifth'erotor comparedrelatively to the inductive resistance, becomes reduced step by step. Insmall motors, 'where current-rushes at start ing are not great, it maybepossible merely to short ci-rcuit the half phasesl, Q, 3 Q F aTb 1f itisnecessary to reduce the stator starting current yet moreythe arrangementof rotor windings indicated in Figure 1, maybe varied as shown inFigure3..

e current value may I In the arrangement of windings shown in Figure 3,the ends of half-phases 3 2 1 are connected not to the mid-points ofhalfphases 1, 3, 2, but to the mid-points of halt phases 1 3 2respectively at points A, C, B, and thismethod of connection gives thefollowing closed circuits:

In each of these circuits the effective electronotive forte is that dueto one quartero'f a 'wholepha'se. a r v For instance, in the 1st circuithalf the valueof theelectro-motive force induced in half-phase 1 isneutralized by'that induced 1n the fourth part A -A of the whole phasewhilst the electro-motive forces induced in halflphases3-8 opposeandneutralize-each other. v y

The currentz' due to theresultant electromotive force-in thecircuit'under'considerat on flows in half-phases 3}, 3 in oppositesenses sothat-the magnetic fields due to the half-phases are-almostwholly compensated so long; as tliephase-conductors are arranged in therotor slots as already indicated. In the portion of the circuitcomprising windings 1, A A the part A 'A compensates the part 1 to theextent of one ha-lf.

All-said in res ectof the 1st circuit-applies equally wel to the 2ndandBrd circuits. I g I I By comparing the corresponding circuits ofFigures 1 and 3it may be seen that the ohmic resistance of each circuitof Figure 3 is greater than that of the respective circuit of Figure 1.p I n in the first scheme. the value of the starting current may bevaried by moving the points of connection A, B, G of Figure 3 in one oriother directionfalong the windings 1 2, 3 respectively; In fact, bymo'vingpoints A, 13,0 nearer. topoints A ,.B C respectively, the. valuesof the resultant electro-motive forcesinthe 1st,.2ndand 3rdclosedcircuits the rotor winding are increased, together with theresultin currents. Conversely by moving points A, 13, (Jim'-therfrom-points KflBlgCh the value "of-the.

starting current is decreased.

3 For instance,with increase of speed the windings may beshort-circuited ,first at points A, BfC and afterwards at points A,

' In] small motors, where current-rushes at starting are notgreat, it"may be possible s E3? by step, the portions of-half-phases. 1

Although the present invention is shown in these drawings as applied tothree-phase rotor windings, it is to be understood that the invention isin no way limited to this particular case, and can be applied tomultiphase rotor windings.

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is:

1. A polyphase rotor for an asynchronous motor in which each phasecomprises two approximately equal windings arranged and connected insuch a manner that the said two windings of each phase oppose and magnetically balance each other, a winding and a portion of the otherwinding of each phase 2, 8, may gradually be short-circuited instead ofthe half-phases 1 being also connected in series with'an adjacent phasewhereby each phase comprises a high ohmlc reslstance and anelectro-motive force generated in a part only of one of said windings iseffective in each phase.

2. A polyphase rotor for an asynchronous motor in which each phasecomprises two approximately equal windings arranged and connected insuch a manner that the said two windings of each phase oppose andmagnetically balance each other, a winding and a portion of the otherwinding of each phase being also connected in series with an adjacentphase whereby each phase comprises a high ohmlc resistance and anelectromotive force generated in a part only of one of said.

windings is effective in each phase, and means whereby one of saidwindings in each phase is short-circuited step by step during thestarting period of the motor.

In testimony that I claim the foregoing as my invention, 1 have signedmy name.

OLAUDIUS SHENFER.

